The present invention provides a device for measuring pressure or flow in a conduit, the device comprising a body having a first pressure chamber within the body communicating with a first aperture in the body; a second pressure chamber within the body communicating with a second aperture in the body spaced from the first aperture; and means for sensing pressure difference between said first and second pressure chambers.

Preferably the body has a nose, a centre section, and a tail; the nose is typically curved or tapered. The

centre section can have generally parallel sides, and the tail can be generally tapered.

There can be more than one aperture, for example, a single forward facing aperture can be provided in the nose, and a set of e. g. 2-6 or more second apertures can be provided, typically in the centre section of the body spaced backwards from the nose. The second apertures could instead be in the tail. More than one (e. g. 2-6) first apertures could be provided.

The first chamber is typically provided in the nose section, and the second chamber is preferably provided in the centre section, but this is only exemplary, and the two chambers can be located at any convenient place on the body; all that is required is that the second aperture is spaced from the first, and is preferably located at a position that is behind the first with respect to the flow of fluid past the device, i. e. downstream of the first aperture.

The means for sensing pressure difference can be any conventional pressure sensor such as a diaphragm differential pressure sensor.

Preferred embodiments of the invention will now be described, referring to the drawings, in which: Fig. 1 is a perspective view of a first device; Fig. 2 is a schematic cross-section of the device of Fig. 1;

Fig. 3 is a side view, partly in section, of a modified form of the foregoing embodiment ; and Fig. 4 is a perspective view of a sock used in Fig. 3.

Referring to Figs. 1 and 2, the device consists of a shaped"fish"10 which is inserted into a conduit. The fish 10 has a nose cap 17, a centre section 18 and a tail section 19. The centre section has an optional mounting bar 12 that connects it to a pipe (not shown).

The mounting bar 12 could optionally be hinged at 13 into the fish 10 in such a way that the fish can be inserted nose first if necessary and the centre of gravity will be slightly upstream of the pivot ensuring that the fish will level out if a minimum flow is experienced and will return to vertical if the flow is switched off. This helps to insert the fish 10 through narrow standpipes, but is not essential.

For very small pipes the fish need not be hinged and could simply be permanently mounted in its own housing plumbed into the flow pipe.

A small aperture 14 at the front of the fish 10 in the nose cap 17 leads to a reservoir 16 of'High Pressure' inside the nose cap 17. Apertures 20 around the sides of the central section 18 of the fish 10 lead to a reservoir 22 of'Low Pressure'in the central section 18 of the fish. The pressures within these two reservoirs 16,22 are compared by a small differential

pressure sensor 24 and their difference is optionally pre-calibrated for a given flow rate for the appropriate size of pipe, or could be calibrated in situ.

The analogue signal from the pressure sensor 24 is carried on two wires 26 up through the mounting bar to the surface where electronics and firmware of conventional design can convert it to a stabilised digital reading for display or recording. The signal can optionally be transmitted electronically (and optionally automatically in real time) by any suitable means to a remote monitoring or control station, where data from numerous meters throughout a water supply system can be co-ordinated and analysed to provide a real time report of the water flow rates and/or pressures at different points in the system, from which leak causes and locations can be derived.

The differential pressure signals can be used as an indicator of the flow rate of the fluid flowing past the fish 10, and can be used as an indicator for leaks in a pipe. High-pressure differentials can mean high flow rates, and vice versa.

The pressure sensor 24 may suitably be a silicon diaphragm differential pressure sensor by Honeywell, which comprises a silicon diaphragm having opposite faces exposed to the respective high and low pressure already.

Figs 3 and 4 illustrate a modified embodiment in which a fish 100 is used which is similar to the fish 10 but, instead of being hinged to a mounting bar, is tethered by flexible lines (or a rigid mounting bar) to a sock assembly 102.

For maximum accuracy of volumetric flow, the cross sectional area of the flow requires to be accurately known. Many pipes are heavily scaled on the inside, making the cross sectional area uncertain. The sock assembly 102 provides a known flow cross section, within which the fish 100 operates.

The sock assembly 102 comprises a hinged perimeter 104 connected to a mounting rod 106 and attached to the upstream end of a fine woven bag 108 which is slightly larger than the pipe diameter at first, and then tapers to a long cylindrical section, smaller than the pipe, in which the fish 100 is located. The sock assembly 102 could be flexible or rigid.

The perimeter 104 is formed of hinged sections with hinges whose rotation is limited by stops. The member 104 can be inserted in a collapsed condition through a standpipe 110; when the bottom of the member 104 engages the bottom of the pipe, the hinges open to fill the inside of the pipe. This ensures that the flow sensor is located in an accurately known flow cross- section.

Modifications and improvements can be incorporated without departing from the scope of the invention.